1. Field of the Invention
The present invention relates to a voice cell transmission method and a system using the method. More particularly, it relates to a voice cell transmission method by which voice cells can be effectively transmitted when transmitting compressed voice traffics through an ATM (Asynchronous transfer mode) network.
2. Description of the Related Art
Recent business networks have the feature such that an ATM technique is used, even in private networks employing the speed of around 1.5 Mbps, and inter-LANs communication and voice traffics are available by a so called low-speed ATM network. In this way, it has been greatly expected to construct an ATM integrated network system where all traffics are carried in even one network.
Especially, there have been various expectations relating to voice traffics. For example, it is expected to obtain high quality equivalent to that of the conventional communication system in an aspect, but to compress voice communication bands by employing a high compression technique, i.e., to reduce communication costs rather than the voice quality in another aspect.
As is typically shown in FIG. 20, a system accomplishing the former expectation may cause influences on the voice quality due to the reduction of the band width used when replacing a conventional TDM net work with a new network. The system accomplishing the latter expectation would influence to increase the transmission delay when pursuing convenience than the tone quality as a result of increasing users of cellar phones in recent years.
Therefore, there was a demand to provide a network, by which these expectations can be flexibly accomplished.
To cope with the above-described expectations, there are two kinds of conventional techniques: the first one is a circuit emulation service (CES); and the second one is a voice and telephony over ATM technique (VTOA). FIG. 21 shows an explanation diagram of the circuit emulation service. In this technique, a constant bit rate (CBR) transmission is possible by assembling a PCM digital voice signal of 64 Kbps into a cell signal, as it is.
A feature of this technique is to provide a communication quality almost equivalent to a time division multiplexing (TDM) transmission method, because of the low speed transmission delay. However, it is technically difficult to introduce a voice compression technique, especially, a soundless compression technique. Therefore, it causes a problem from a view point of efficiently using communication bands.
On the other hand, in the second technique, i.e., the VTOA technique, a short cell format is prescribed for each of plural communication channels, as shown in FIG. 22. In FIG. 22, the short cell format consists of a channel number CN to which the short cell is belonging, and voice signal data VSD, for example.
Further, the short cells generated from the plural communication channels are multiplexed, the multiplexed short cells are provided on a payload of 48 octets, and a header H and a control section C, which indicates how many short cells are included are added. Accordingly, a standard ATM cell can be constructed, having a format recommended by ITU-T or ATM forum.
In here, it is assumed to concentrate plural voice channels in a payload of one standard cell. However, in a network for such a general private company as having a voice data source of several channels, a probability of concentrating traffics to one route is low. Therefore, it is difficult to expect an efficiency of multiplexing in a payload of the standard cell.
As described above, when considering a voice and data integrated ATM network for general people, the number of voice channels is small, especially, in a small-scaled location. Therefore, it is not effective to use an architecture, in which plural channels are provided in one standard ATM cell, such as VTOA. On the other hand, when making only one channel into a cell, a time required to assemble the channel into a cell is increased, and therefore, it becomes difficult to cope with the limitation of delay time in a network.
Accordingly, it is an object of the present invention to provide a voice cell transmission method employing the VTOA architecture to minimize the transmission delay time when transmitting the voice cells.
To achieve the above-described object of the present invention, it can be realized by a voice transmission method, in an ATM transmission system for transmitting a voice traffic, which is compressed, and is provided on a payload of a standard cell in a short cell format, comprising the steps of forming voice frames in every predetermined period of a talk-spurt of one voice channel, and providing the formed voice frames continuously on the payload of the standard cell.
In one preferred mode of the present invention, a number of the voice frames of the one voice channel provided on the standard cell are dynamically varied according to a status of the network.
Alternatively, in other preferred mode of the present invention, when communications for plural voice channels are performed, a number of the voice frames provided on the payload of the standard cell including a header frame of the talk-spurt is differed in each of the plural voice channels.
Further, in one mode of the present invention, a number of the voice frames provided on the payload of the standard cell is fixed in each of the plural voice channels.
Furthermore, in other mode of the present invention, a number of the voice frames provided on the payload of the standard cell in each of the plural voice channels is differed in every talk-spurt.
Additionally, in other mode of the present invention, when the voice frames include an end voice frame, and there are extra spaces for providing voice frames on the payload of the standard cell, standard cells of other voice channels are not taken preference.
In one mode of the present invention, a number of the voice frames corresponding to one voice channel provided on one standard cell is dynamically varied according to priority of a specific call.
In addition to the above-described explanation, other objects of the present invention become clear by the description for explaining embodiments according to the attached drawings, in addition to the above-described explanations.